A weak rand currency has spurred a stream of South African players to leave the country for teams in Europe.
"The player made a personal request to be released to further his career abroad and we felt we couldn’t stand in his way while. We also couldn’t match the offer he received," said Rudolf Straeuli, chief executive officer of the Lions Rugby Company.
Straeuli said de Klerk would move to Sale once the Super Rugby season had concluded.
"Faf is still very important in our Super Rugby campaign as he plays a vital role in our squad system."
De Klerk joined the Lions in 2014 and has made 58 Super Rugby appearances, scoring 12 tries.
